Posted
by
Soulskill
on Tuesday December 22, 2015 @11:25PM
from the back-in-business dept.

hypnosec writes: Oak Ridge National Laboratory has successfully produced 50 grams of plutonium-238, an isotope that produces heat without a lot of other, problematic radiation. This makes it suitable for use in radioisotope thermoelectric generators, which can power space probes. The new sample effectively revives the U.S.'s end-to-end plutonium-238 production capabilities, which have been dormant for around 30 years since work was stopped at the Savannah River Plant in South Carolina. The ORNL is optimistic this important milestone will pave the way for regular production of the material, ensuring constant supply for NASA's future missions.

Sounds like a pretty weak response from NASA "tested to withstand intense heat" and the Energy department guy "the RTG can't explode like a bomb". That's not the problem. You're strapping a bunch of highly toxic and radioactive material *onto* a huge bomb (aka rocket). So where's the response that says they've tested it to make sure it can survive having the bomb detonate, as sometimes happens?

If they *haven't* tested the RTG to survive the detonation of the launch vehicle, then I would say the protesters

There have been several known accidents involving RTG-powered spacecraft:

The first one was a launch failure on 21 April 1964 in which the U.S. Transit-5BN-3 navigation satellite failed to achieve orbit and burned up on re-entry north of Madagascar.[26] The 17,000 Ci (630 TBq) plutonium metal fuel in its SNAP-9a RTG was injected into the atmosphere over the Southern Hemisphere where it burned up, and traces of plutonium-238 were detected in the area a few months later.

The second was the Nimbus B-1 weather satellite whose launch vehicle was deliberately destroyed shortly after launch on 21 May 1968 because of erratic trajectory. Launched from the Vandenberg Air Force Base, its SNAP-19 RTG containing relatively inert plutonium dioxide was recovered intact from the seabed in the Santa Barbara Channel five months later and no environmental contamination was detected.[27]

In 1969 the launch of the first Lunokhod lunar rover mission failed, spreading polonium 210 over a large area of Russia [28]

The failure of the Apollo 13 mission in April 1970 meant that the Lunar Module reentered the atmosphere carrying an RTG and burned up over Fiji. It carried a SNAP-27 RTG containing 44,500 Ci (1,650 TBq) of plutonium dioxide which survived reentry into the Earth's atmosphere intact, as it was designed to do, the trajectory being arranged so that it would plunge into 6–9 kilometers of water in the Tonga trench in the Pacific Ocean. The absence of plutonium-238 contamination in atmospheric and seawater sampling confirmed the assumption that the cask is intact on the seabed. The cask is expected to contain the fuel for at least 10 half-lives (i.e. 870 years). The US Department of Energy has conducted seawater tests and determined that the graphite casing, which was designed to withstand reentry, is stable and no release of plutonium should occur. Subsequent investigations have found no increase in the natural background radiation in the area. The Apollo 13 accident represents an extreme scenario because of the high re-entry velocities of the craft returning from cis-lunar space (the region between Earth's atmosphere and the Moon). This accident has served to validate the design of later-generation RTGs as highly safe.

Mars 96 launched by Russia in 1996, but failed to leave Earth orbit, and re-entered the atmosphere a few hours later. The two RTGs onboard carried in total 200 g of plutonium and are assumed to have survived reentry as they were designed to do. They are thought to now lie somewhere in a northeast-southwest running oval 320 km long by 80 km wide which is centred 32 km east of Iquique, Chile.[29]

I agree that Space-bound RTGs have a good track record against reentry concerns, as they are generaly specifically designed to deal with that. But only one of your accidents (possibly two) involved subjecting the RTG to an actual explosion:

The Lunokhod-0 mission, which did *exactly* what the protestors here were afraid ofand the Nimbus B-1 mission, which was an intentional destruction due to an erratic flightpath. and may well have been carried out in a manner designed to avoid vaporizing the RTG.

> Progress involves riskCertainly. And rational beings weigh the risk against the potential gains, and take steps to mitigate unreasonable risks>and it's space or nothingBullshit. I'm a huge space enthusiast, but I also recognize that it's incredibly unlikely that we're going to find anything particularly valuable to humanity on timescales less than a century, and probably closer to thousands of years. Timescales that make "I can't be bothered to avoid poisoning inhabited areas" a pretty weak argumen

Nothing went wrong. Yay. Usually nothing serious goes wrong, but that doesn't mean you should ignore the consequences of various common ways that they *might* go wrong. Because sooner or later something *will* go wrong - the risk of catastrophic failure is always there, and sometimes the secondary consequences can be severe.

Ummm yeah. But food for thought is that many or the materials used in the manufacture and the waste products it produces are toxic or poisonous, and ORNL is built on top of karst. If you live in the area, don't drink the water. Or eat anything that grows in it.

Obviously the rad deer are not a fixed population, they get continually contaminated by something that should be found and cleaned up.
They shame really is that they don't let the hunters keep them, psychopaths deserve to be poisoned.

Pu-238 is a great thermal heating material. A gram of Pu-238 generates about 500 mW of heat through radioactive decay and initial release of alpha particles (plain old helium nuclei). Helium nuclei are large and heavy, and are stopped by even a sheet of paper. The decay chain for Pu-238 is mostly a number of alpha particle releases and a slow and gradual walk toward Pb (lead).

In metallic or solid ceramic form, Pu-238 is safe to handle. You could arguably carry around a chunk of it, but the thermal heat generated is significant and you might get burned. Machining it is straightforward, the dust needs to be controlled.

Err... I am not a nuclear scientist and I didn't even stay in a hotel last night but I'm pretty sure Pu-238 emits alpha particles which are not harmless but just don't eat 'em. (You put that cookie in your pocket.) So, as a weapon... What, are we going to duct tape the plutonium to a stick and hit people with it so we can... What? Burn them? We can save time, effort, and money just by hitting them with a stick.

Yes, it is radioactive, and yes, it is a very nasty heavy metal... but there are still pacemakers ticking away with this stuff as the "battery" 25+ years later.

I wonder if Pu-238 might have some use in areas where batteries are needed and extremely hard to replace other than space projects. Definitely not for a battery for a smartphone, because we don't want Youtubers like TechRax to get radiation poisoning, but airline flight data recorders come to mind.

Terrible idea. First, flight data recorders have easy access to ample power (from the aircraft) for 99.9% of their life... It's only that 0.1% of the time that batteries would have to kick-in, and rechargeable NiMH work great and can last for decades in such an easy duty-cycle.

Secondly, an RTG costs more than your HOUSE, and is huge.

Third, PU-238 doesn't make electricity, just heat, so you need a full heat engine in there, somewhere. A simple Peltier works, but they're maybe 90% efficient, so you're talking extremely high temperatures to generate a useful amount of electricity, which need to be conducted out somewhere. That means your iPhone or flight data recorder power by PU-238 will have to run several-hundred degrees hotter than you'd find comfortable...

It does make sense though. I was assuming by "thermal-electric" generator that a heat engine was involved in the process with a reverse Peltier method.

In general, nuclear (be it fission, elements for radioactive decay, etc) is to be way underused, just due to the sheer and unwarranted fear of it. Yes, it has its dangers, but if used right, it can solve a lot of the world's major problems. It doesn't suffer fools gladly... but neither did steam energy, nor early internal combustion prototypes.

The difference though, is that when steam and ICE failed to suffer a fool, it was only the fool and possibly a few bystanders that were harmed. When a nuclear power source fails to suffer a fool, you've generally got some nasty environmental contamination on your hands, and it's unlikely that anyone is going to be willing to clean it up even if they are able. Fukushima springs to mind, but even a plutonium pacemaker that doesn't get removed before cremation is going to be a nasty little local issue. Not t

Very few searches last that long, and power to the FDR pretty much only helps in large water body crashes. If it's in a field somewhere, you just go around with a metal detector until you find something. Even underwater, you're assuming only power is running out, when a high-speed crash could damage the pinger, and being buried under debris could obscure and render it ineffective.

Doubling the capacity of the batteries would add maybe $20 to the cost of

Most if not all of the Soviet-era lighthouse RTGs used Sr-90, an isotope of strontium rather than Pu-238 as a heat source. It required heavier shielding than a Pu-238 RTG but in land-based generators the extra mass of the case didn't affect its capabilities the way an RTG to be mounted on a spacecraft would.

Sr-90 can be sourced from spent fuel from power plants and the Soviets had a fuel reprocessing capability to produce Sr-90 in quantity. The Russian government is looking to upgrade and expand their existing fuel reprocessing operations, in part to supply their next-generation series of fast reactors like the BN-800 with recycled spent fuel.

Hmm. it's an arrangement of letters representing an easily pronounceable sound-pattern with an obvious conceptual meaning. In what way is it not a word?

Oh, you probably meant it's not a formally recognized word. Gosh, it's a good thing those creators of the Oxford English Dictionary came along. Before then humans must have been limited to communicating with grunts and gestures.

It's what you say when you're calling someone a potato-head. You Tuber! That said, I'd lie and say I'm sorry but I'm not. If I were sorry then I'd not do what I'm about to do. In fact, I am so not sorry that I'm typing this out in advance. So, it's more a warning...

Have some "Maine humor." (Maine grows a lot of potatoes. You've eaten some if you live in the US, probably. See McDonald's fries for one example.)

So, Mommy, Daddy, and Baby Potato were walking downtown one day. And Baby Potato is walking along wi

Impressive! that's just over 3 horsepower of sustained energy for 2.3 kW.

If I understand this correctly (and discounting AC/DC conversion loss) : For an electric vehicle, Level 1 charging provides 1.8 kW - or 4.5 miles of range per hour of charging. Level 2 charging provides 3.3 kW - or 12 miles of range per hour. Level 2 charging can go to 6.6 kW - or 26 miles of range per hour.

So depending on how often you drive, where, and length, your next EV could have anywhere from 4kg to 12kg of Pu-238 installed...

The process described starts with a solid Neptunium-237 oxide, mixes it with Aluminum, presses it into pellets, irradiates it, chemically separates the Plutonium-238, and then processes it back into a solid oxide. They don't say where the Neptunium itself comes from, other than mentioning an existing inventory. It can be recovered from spent fuel, using another convoluted process starting with solid oxides.

Creating 237Np would be a far more direct process with a LFTR [wikipedia.org], where the 2% of the fuel which does not fission mostly finds its way to be this very isotope. (The remainder become short-lived fission products.) Naturally, processing a liquid is easier than going through multiple solid oxide steps, and lends itself to a continuous process capable of producing 238Pu in volume. It would be far more interesting if ORNL were developing the processes for this instead.

This is the only comment (out of 49 so far) in this thread which is intelligent, useful, and constructive. There was a time (oh you youngsters!) when this was the rule, not the exception, on slashdot. The hamster comment deserves credit for humor, though.

In the past week, I've gone over a few old articles and read every one of the comments. Two subjects spring to mind. The first is Mozilla with Firefox and the other is VMware. A common theme was that Firefox would never catch on with the masses and IE would remain king on the desktop. VMware was useless, a fad, vaporware that couldn't work, and virtual machines would never be of interest to anyone in the future, ever.

I used to have a much lower UID but I got busy, stopped participating, lost the email addre

Mars-2020 and Europa-2025 have dibs on two of the missions. And you have to decide many years in advance which power source to use.

Jupiter is border line solar. Most of its probes have been nuclear. But Juno due to arrive shortly has 180 feet of solar panels. Juno is designed to last only a short time because it is flying through Jupiters highly toxic geomagnetic fields to study them.

I recall NASAs supply partly came from decommissioned Soviet warheads. But that process is now over.

You do know that the vast majority of the US nuclear stockpile is Plutonium-based weapons, right?

Plutonium takes far less material to create a critical mass, which makes for a lighter weapon. A lighter weapon means you don't need a big-dick huge fucking rocket to put the thing where you want it to be, and instead can use smaller rockets and missiles for deployment. And, if you aren't under the microscope, making Plutonium is easier than separating an ass ton of U235 from an even bigger shit ton of U238 th

Plutonium takes far less material to create a critical mass, which makes for a lighter weapon. A lighter weapon means you don't need a big-dick huge fucking rocket to put the thing where you want it to be, and instead can use smaller rockets and missiles for deployment,

Let's not get carried away into orgasms of hyperbole. The critical mass of fissionable is not the governing determinant of the weight of the weapon. For U-235, the critical mass of a simplistic untamped sphere is 52 kg; for Pu-239 it is 9 kg.

Actually, from Wikipedia https://en.wikipedia.org/wiki/... [wikipedia.org] Little Boy yield - 13-18 kt TNTFat Man yield = 20-22 kt TNTGiven that they were some of the first nuclear weapons ever made, I'm guessing those are ranged estimates rather than tunable yields, meaning that Fat Man had somewhere between 11% and 70% higher yield for that 16% greater mass.

We're also talking about early bomb designs that were very much proof-of-concept weapons. I suspect that later weapons, especially tactical nukes, are considerably mor

And? Sorry I don't see how that's relevant. Yes, most nuclear weapons (and reactors) have frankly *horrible* conversion rates in the single digit range. Knowing that, you can either work to increase the conversion efficiency (hence things like fission-fusion bombs where the fusion primarily provides a rich neutron source for further fissioning), or increase the fissile payload. Neither is directly relevant to the yields of plutonium versus uranium weapons, though I'll concede that the ease of enhancing

no, go look it up. Neither or the US bombs were efficient at all, and one was very nearly a fizzle. The total amount of material that underwent fission (including both bombs) was on the order of 1 - 5 GRAMS if I've got it right.

You don't have it right. Each bomb fissioned about 1 kg of material, for the Fat Man this makes it about 20% efficient. That is pretty good for a first design. Fission bombs are generally no more than 50% efficient, usually less.

Pu-238 = great source of heat, not a great source of boom.Pu-239 = great source of boom, not a great source of heat.Pu-240, Pu-241 = not a great source of boom or heat.

Pu-238 is not used in weapons specifically because it fissions too fast spontaneously. That's why it makes so much heat. And, because of this, your weapon would have a significant portion of it reduced to not-plutonum and neutron poisons by the time you want to use it.

A not so minor point which deserves mention: the Pu-239 must be >90% pure for weapons. Reactor grade plutonium from spent fuel is absolutely useless for weapons. The only practical method of creating it is to briefly expose U-238 to a neutron flux, separate the Pu-239 out, and repeat many times, which requires a specialized reactor. Pu-239 can't just be pulled out of spent fuel; the plutonium isotopes are too close in mass to make isotopic separation viable.

Yes, plutonium from spent fuel, at a very high level, is where the plutonium for weapons came from.

What you're not saying, and the GP did, is that the 'spent' fuel wasn't actually spent, because it was only in the reactor for a very short (and uneconomical) time so that the U238 captured a neutron to become U239, then decayed to Pu239. You leave it in too long, it captures another neutron and becomes Pu240, which ruins the plutonium for weapons purposes.

Most of the reactors built to produce plutonium in the US did not generate electricity. Their sole purpose was to produce plutonium, and everything else (IE many gigawatts of heat that could theoretically have been used for power-generation) was a waste product. IMO it's extremely misleading to refer to such a source as "spent fuel", because it implies that a typical nuclear power station's spent fuel (IE the waste byproduct of electrical power generation) could be used as a source of weapons-grade plutoniu

Pu-238 = great source of heat, not a great source of boom.Pu-239 = great source of boom, not a great source of heat.Pu-240, Pu-241 = not a great source of boom or heat.

It's not just that Pu-238 is hot, it's also that it has really benign decay characteristics. It's an alpha emitter (alpha particles are very easy to block and convert to head without getting X rays) and decays to U-234. That's got a much longer half-life (200,000 years) and is also an alpha emitter, and decays to Thorium 230. That's got a mod

Actually Pu238 doesn't fission spontaneously. Fission typically refers to the fragmentation of the nucleus into two roughly equal-sized fragments, which thanks to the lower nucleon mass (=higher binding energy) at lower nucleon counts, multiplied by the large number of nucleons involved, results in considerable mass loss and a correspondingly large energy release.

In contrast Pu238 undergoes alpha decay, where it ejects just four nucleons as an alpha particle (helium 4 nucleus), only very slightly reducing

Pu-238 is not used in weapons specifically because it fissions too fast spontaneously. That's why it makes so much heat.

No, it makes so much heat because it undergoes alpha decay with an 87.77 year half-life. Its half-life for spontaneous fission is 47.7 billion years, so for each fission it produces 500 million alpha decays. Only 0.00001% of the heat is from fission. It would be a whole lot less useful if it were producing all that heat from fission since it would be similar to a nuclear reactor and the extremely intense neutron flux would require very heavy shielding.

Assuming they know more about nuclear materials than some Slashdot anonymous coward, which is likely, they won't give a shit because they'll know that this is the kind of plutonium you build space probes from, not the kind you make nuclear weapons from. 238 is not 235.

Who gives a shit what foreigners think about the US. It's of no consequence.

Wrong. The U.S. does more than 4 TRILLION dollars a year of business with the rest of the world. Its scientists and schools collaborate with institutions around the world to advance the sum total of human knowledge, and its schools educate and shape the views of many members of the educated and ruling classes in countries around the world. It also has foreign policy interests that range from offering humanitarian relief after natural disasters and combating human trafficking to building coalitions agains

you are missing the point. the USA can do what it wants without regard to anything you just said with impunity. anyone or any nation hat doesn't like it can fuck off or maybe even get droned or regime changed.

Well, you could probably attach it to a stick and hit people with it. I mean, if we're going to be pedantic here (and we ARE - it's what we do) then it can be used for weapons. It just probably won't be a very effective weapon. They should cover a thin layer with a chicken-wire reinforced ceramic. I can put it at the end of my bed to keep my feet warm or maybe have varied amounts so that I can use one as an "always" on teapot heater.

This is also why they don't let me near any of the stuff. However, I'd buy

Actually, less than that - it generates 114W/kg in decay heat, versus ~500W/kg for Pu238

It also has a non-negligible spontaneous fission rate, and emits gamma radiation. Less of an issue in space where everything is being radiation bombarded anyway, but it makes it a generally less attractive RTG fuel.